General:
* Axe: This is probably the most common slang term, often used by rock musicians.
* Six-string: Refers to the number of strings on a standard guitar.
* Wood: A more informal and somewhat dated term.
* Fretboard: This term refers to the neck of the guitar, but can also be used as slang for the guitar itself.
* Strum-stick: A playful, informal term.
More specific:
* Tele: Short for Telecaster, a type of electric guitar.
* Strat: Short for Stratocaster, another popular electric guitar model.
* Les Paul: A specific type of electric guitar.
* Gibson: Refers to the brand of guitars, often used as a slang term for the guitar itself.
Regional:
* Rickenbacker: Sometimes referred to as "Ricky" in specific communities.
The best slang term to use really depends on the situation and who you're talking to!